Homo erectus appeared about two million years ago in East Africa (where it is dubbed Homo ergaster) and, in several early migrations, it spread throughout Africa and Eurasia. It was likely the first hominin to live in a hunter-gatherer society and to control fire. An adaptive and successful species, Homo erectus persisted for almost 2 million years before suddenly becoming extinct about 70,000 years ago (0.07 Ma)—perhaps a casualty of the Toba supereruption catastrophe.

Homo sapiens sapiens, or anatomically modern humans, emerged about 200,000 years ago (0.2 Ma) in East Africa (see Omo remains). There is division among scholars as to when H. s. sapiens became behaviorally modern; the debate is: modern behavior developed 1) simultaneously with anatomical development, or 2) separately, and was complete by 50,000 years ago (see Modern human behavior). Homo sapiens sapiens is the only surviving species and subspecies of the genus Homo; all others have become extinct.

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Evolutionary tree chart emphasizing the subfamily Homininae and the tribe Hominini. After diverging from the line to Ponginae the early Homininae split into the tribes Hominini and Gorillini. The early Hominini split further, separating the line to Homo from the lineage of Pan. Currently, tribe Hominini designates the subtribesHominina, containing genus Homo; Panina, genus Pan; and Australopithecina, with several extinct genera—the subtribes are not labelled on this chart.

The Latin noun homō (genitive hominis) means "human being" or "man" in the generic sense of "human being, mankind".[11] The binomial nameHomo sapiens was coined by Carl Linnaeus (1758).[12] Names for other species of the genus were introduced beginning in the second half of the 19th century (H. neanderthalensis 1864, H. erectus 1892).

Even today, the genus Homo has not been properly defined.[13][14][15] Since the early human fossil record began to slowly emerge from the earth, the boundaries and definitions of the genus Homo have been poorly defined and constantly in flux. Because there was no reason to think it would ever have any additional members, Carl Linnaeus did not even bother to define Homo when he first created it for humans in the 18th century. The discovery of Neanderthal brought the first addition.

A model of the evolution of the genus Homo over the last 2 million years (vertical axis). The rapid "Out of Africa" expansion of H. sapiens is indicated at the top of the diagram, with admixture indicated with Neanderthals, Denisovans, and unspecified archaic African hominins.[16]

The genus Homo was given its taxonomic name to suggest that its member species can be classified as human. And, over the decades of the 20th century, fossil finds of pre-human and early human species from late Miocene and early Pliocene times produced a rich mix for debating classifications. There is continuing debate on delineating Homo from Australopithecus—or, indeed, delineating Homo from Pan, as one body of scientists argue that the two species of chimpanzee should be classed with genus Homo rather than Pan. Even so, classifying the fossils of Homo coincides with evidences of: 1) competent human bipedalism in Homo habilis inherited from the earlier Australopithecus of more than four million years ago, (see Laetoli); and 2) human tool culture having begun by 2.5 million years ago.

From the late-19th to mid-20th century, a number of new taxonomic names including new generic names were proposed for early human fossils; most have since been merged with Homo in recognition that Homo erectus was a single and singular species with a large geographic spread of early migrations. Many such names are now dubbed as "synonyms" with Homo, including Pithecanthropus,[17]Protanthropus,[18]Sinanthropus,[19]Cyphanthropus,[20]Africanthropus,[21]Telanthropus,[22]Atlanthropus,[23] and Tchadanthropus.[24]

Classifying the genus Homo into species and subspecies is subject to incomplete information and remains poorly done. This has led to using common names ("Neanderthal" and "Denisovan") in even scientific papers to avoid trinomial names or the ambiguity of classifying groups as incertae sedis (uncertain placement)—for example, H. neanderthalensis vs. H. sapiens neanderthalensis, or H. georgicus vs. H. erectus georgicus.[25] Some recently extinct species in the genus Homo are only recently discovered and do not as yet have consensus binomial names (see Denisova hominin and Red Deer Cave people).

John Edward Gray (1825) was an early advocate of classifying taxa by designating tribes and families.[26] Wood and Richmond (2000) proposed that Hominini ("hominins") be designated as a tribe that comprised all species of early humans and pre-humans ancestral to humans back to after the chimpanzee-human last common ancestor; and that Hominina be designated a subtribe of Hominini to include only the genus Homo—that is, not including the earlier upright walking hominins of the Pliocene such as Australopithecus, Orrorin tugenensis, Ardipithecus, or Sahelanthropus.[27] Designations alternative to Hominina existed, or were offered: Australopithecinae (Gregory & Hellman 1939) and Preanthropinae (Cela-Conde & Altaba 2002);[28][29][30] and later, Cela-Conde and Ayala (2003) proposed that the four genera Australopithecus, Ardipithecus, Praeanthropus, and Sahelanthropus be grouped with Homo within Hominina.[31]

A fossil jawbone dated to 2.8 million years ago which may represent an intermediate stage between Australopithecus and Homo was discovered in 2015 in Afar, Ethiopia.[35] Some authors would push the development of Homo past 3 Mya, by including Kenyanthropus (a fossil dated 3.2 to 3.5 Mya, usually classified as an australopithecine species) into the genus Homo.[36]

The most salient physiological development between the earlier australopithecine species and Homo is the increase in cranial capacity, from about 450 cm3 (27 cu in) in A. garhi to 600 cm3 (37 cu in) in H. habilis. Within the genus Homo, cranial capacity again doubled from H. habilis through Homo ergaster or H. erectus to Homo heidelbergensis by 0.6 million years ago. The cranial capacity of H. heidelbergensis overlaps with the range found in modern humans.

Homo erectus has often been assumed to have developed anagenetically from Homo habilis from about 2 million years ago. This scenario was strengthened with the discovery of Homo erectus georgicus, early specimens of H. erectus found in the Caucasus, which seemed to exhibit transitional traits with H. habilis. As the earliest evidence for H. erectus was found outside of Africa, it was considered plausible that H. erectus developed in Eurasia and then migrated back to Africa. Based on fossils from the Koobi Fora Formation, east of Lake Turkana in Kenya, Spoor et al. (2007) argued that H. habilis may have survived beyond the emergence of H. erectus, so that the evolution of H. erectus would not have been anagenetically, and H. erectus would have existed alongside H. habilis for about half a million years (1.9 to 1.4million years ago), during the early Calabrian.[37]

Some of H. ergaster migrated to Asia, where they are named Homo erectus, and to Europe with Homo georgicus. H. ergaster in Africa and H. erectus in Eurasia evolved separately for almost two million years and presumably separated into two different species.

Homo rhodesiensis, who were descended from H. ergaster, migrated from Africa to Europe and became Homo heidelbergensis and later (about 250,000 years ago) Homo neanderthalensis and the Denisova hominin in Asia. The first Homo sapiens, descendants of H. rhodesiensis, appeared in Africa about 250,000 years ago. About 100,000 years ago, some H. sapiens sapiens migrated from Africa to the Levant and met with resident Neanderthals, with some admixture.[38] Later, about 70,000 years ago, perhaps after the Toba catastrophe, a small group left the Levant to populate Eurasia, Australia and later the Americas. A subgroup among them met the Denisovans[39] and, after further admixture, migrated to populate Melanesia. In this scenario, non-African people living today are mostly of African origin ("Out of Africa model"). However, there was also some admixture with Neanderthals and Denisovans, who had evolved locally (the "multiregional hypothesis"). Recent genomic results from the group of Svante Pääbo also show that 30,000 years ago at least three major subspecies coexisted: Denisovans, Neanderthals and anatomically modern humans.[40] Today, only H. sapiens remains, with no other extant species.

The species status of H. rudolfensis, H. ergaster, H. georgicus, H. antecessor, H. cepranensis, H. rhodesiensis, H. neanderthalensis, Denisova hominin, Red Deer Cave people, and H. floresiensis remains under debate. H. heidelbergensis and H. neanderthalensis are closely related to each other and have been considered to be subspecies of H. sapiens. Recently, nuclear DNA from a Neanderthal specimen from Vindija Cave has been sequenced using two different methods that yield similar results regarding Neanderthal and H. sapiens lineages, with both analyses suggesting a date for the split between 460,000 and 700,000 years ago, though a population split of around 370,000 years is inferred. The nuclear DNA results indicate about 30% of derived alleles in H. sapiens are also in the Neanderthal lineage. This high frequency may suggest some gene flow between ancestral human and Neanderthal populations due to mating between the two.[41]

Homo naledi was discovered near Johannesburg, South Africa in 2013 and announced on 10 September 2015. Fossils indicate the hominid was 1.45-1.5 meters tall and had a small brain.[42] The fossils have yet to be dated.[43]

Wakeley, J (2008). "Complex speciation of humans and chimpanzees". Nature. 452 (7184): E3–4. doi:10.1038/nature06805. PMID18337768. "Patterson et al. suggest that the apparently short divergence time between humans and chimpanzees on the X chromosome is explained by a massive interspecific hybridization event in the ancestry of these two species. However, Patterson et al. do not statistically test their own null model of simple speciation before concluding that speciation was complex, and—even if the null model could be rejected—they do not consider other explanations of a short divergence time on the X chromosome. These include natural selection on the X chromosome in the common ancestor of humans and chimpanzees, changes in the ratio of male-to-female mutation rates over time, and less extreme versions of divergence with gene flow. I therefore believe that their claim of hybridization is unwarranted." see current estimates regarding complex speciation.

^The word "human" itself is from Latin humanus, an adjective formed on the root of homo, thought to derive from a Proto-Indo-European word for "earth" reconstructed as *dhǵhem-. dhghem The American Heritage Dictionary of the English Language: Fourth Edition. 2000.

^Linné, Carl von (1758). Systema naturæ. Regnum animale. (10 ed.). pp. 18, 20. Retrieved 19 November 2012.. Note: In 1959, Linnaeus was designated as the lectotype for Homo sapiens (Stearn, W. T. 1959. "The background of Linnaeus's contributions to the nomenclature and methods of systematic biology", Systematic Zoology 8 (1): 4-22, p. 4) which means that following the nomenclatural rules, Homo sapiens was validly defined as the animal species to which Linnaeus belonged.

^"African man", used by T. F. Dreyer (1935) for the Florisbad Skull he found in 1932 (also Homo florisbadensis or Homo helmei). Also the genus suggested for a number of archaic human skulls found at Lake Eyasi by Weinert (1938). Leaky, Journal of the East Africa Natural History Society' (1942), p. 43.

^from Atlanthropus mauritanicus, name given to the species of fossils (three lower jaw bones and a parietal bone of a skull) discovered in 1954 to 1955 by Camille Arambourg in Tighennif, Algeria. Arambourg, C. (1955). "A recent discovery in human paleontology: Atlanthropus of ternifine (Algeria)". American Journal of Physical Anthropology. 13 (2): 191–201. doi:10.1002/ajpa.1330130203.

^J. E. Gray, "An outline of an attempt at the disposition of Mammalia into Tribes and Families, with a list of genera apparently appertaining to each Tribe", Annals of Philosophy', new series (1825), pp. 337–344.

^In 2010, evidence was presented that seems to attribute the use of stone tools to Australopithecus afarensis, close to a million years before the first appearance of Homo. McPherron, S. P.; Alemseged, Z.; Marean, C. W.; Wynn, J. G.; Reed, D.; Geraads, D.; Bobe, R.; Bearat, H. A. (2010). "Evidence for stone-tool-assisted consumption of animal tissues before 3.39 million years ago at Dikika, Ethiopia". Nature. 466: 857–860. doi:10.1038/nature09248. PMID20703305. "The oldest direct evidence of stone tool manufacture comes from Gona (Ethiopia) and dates to between 2.6 and 2.5 million years (Myr) ago. [...] Here we report stone-tool-inflicted marks on bones found during recent survey work in Dikika, Ethiopia [... showing] unambiguous stone-tool cut marks for flesh removal [..., dated] to between 3.42 and 3.24 Myr ago [...] Our discovery extends by approximately 800,000 years the antiquity of stone tools and of stone-tool-assisted consumption of ungulates by hominins; furthermore, this behaviour can now be attributed to Australopithecus afarensis."

^"A partial maxilla assigned to H. habilis reliably demonstrates that this species survived until later than previously recognized, making an anagenetic relationship with H. erectus unlikely. The discovery of a particularly small calvaria of H. erectus indicates that this taxon overlapped in size with H. habilis, and may have shown marked sexual dimorphism. The new fossils confirm the distinctiveness of H. habilis and H. erectus, independently of overall cranial size, and suggest that these two early taxa were living broadly sympatrically in the same lake basin for almost half a million years." Spoor, F; Leakey, M.G; Gathogo, P.N; Brown, F.H; Antón, S.C; McDougall, I; Kiarie, C; Manthi, F.K.; Leakey, L.N. (2007). "Implications of new early Homo fossils from Ileret, east of Lake Turkana, Kenya". Nature. 448 (7154): 688–691. doi:10.1038/nature05986. PMID17687323.

DiMaggio, Erin N.; Campisano, Christopher J.; Rowan, John; et al. (March 20, 2015). "Late Pliocene fossiliferous sedimentary record and the environmental context of early Homo from Afar, Ethiopia". Science. Washington, D.C.: American Association for the Advancement of Science. 347 (6228): 1355–1359. doi:10.1126/science.aaa1415. ISSN0036-8075. PMID25739409. Hominins with "proto-Homo" traits may have lived as early as 2.8 million years ago, as suggested by a fossil jawbone classified as transitional between Australopithecus and Homo discovered in 2015.

^Haviland, William A.; Walrath, Dana; Prins, Harald E. L.; McBride, Bunny (2007). Evolution and Prehistory: The Human Challenge (8th ed.). Belmont, CA: Thomson Wadsworth. p. 162. ISBN978-0-495-38190-7.H. erectus may have appeared some 2 million years ago. Fossils dated to as much as 1.8 million years ago have been found both in Africa and in Southeast Asia, and the oldest fossils by a narrow margin (1.85 to 1.77 million years ago) were found in the Caucasus, so that it is unclear whether H. erectus emerged in Africa and migrated to Eurasia, or if, conversely, it evolved in Eurasia and migrated back to Africa.

^Curnoe, Darren (June 2010). "A review of early Homo in southern Africa focusing on cranial, mandibular and dental remains, with the description of a new species (Homo gautengensis sp. nov.)". HOMO - Journal of Comparative Human Biology. Amsterdam, the Netherlands: Elsevier. 61 (3): 151–177. doi:10.1016/j.jchb.2010.04.002. ISSN0018-442X. PMID20466364. A species proposed in 2010 based on the fossil remains of three individuals dated between 1.9 and 0.6 million years ago. The same fossils were also classified as H. habilis, H. ergaster or Australopithecus by other anthropologists.

^The type fossil is Mauer 1, dated to ca. 0.6 million years ago. The transition from H. heidelbergensis to H. neanderthalensis at about 0.35 to 0.25 million years ago is largely conventional. Relevant examples are fossils found at Bilzingsleben (also classified as Homo erectus bilzingslebensis).

^Bischoff, James L.; Shamp, Donald D.; Aramburu, Arantza; et al. (March 2003). "The Sima de los Huesos Hominids Date to Beyond U/Th Equilibrium (>350 kyr) and Perhaps to 400–500 kyr: New Radiometric Dates". Journal of Archaeological Science. Amsterdam, the Netherlands: Elsevier. 30 (3): 275–280. doi:10.1006/jasc.2002.0834. ISSN0305-4403. The first humans with "proto-Neanderthal traits" lived in Eurasia as early as 0.6 to 0.35 million years ago (classified as H. heidelbergensis, also called a chronospecies because it represents a chronological grouping rather than being based on clear morphological distinctions from either H. erectus or H. neanderthalensis), with the first "true Neanderthals" appearing between 0.25 and 0.2 million years ago.